Diverse molecules with cytotoxic activity against cancer cells have been isolated from the polar extracts of different parts of various hawthorn species that grow around the world. In Mexico, hawthorn (Crataegus gracilior) is popularly consumed, but its content of anticancer substances has never been evaluated. Because antitumor substances have been identified in polar and nonpolar extracts of many plants, we evaluated the cytotoxic activity against breast cancer cells of petroleum ether, ethanol, and water extracts of the leaves and stems of C. gracilior. In contrast to other hawthorn species that contain anti-tumor substances in polar extracts, the petroleum ether extract (but not the ethanol or water extracts) of C. gracilior had cytotoxic properties (IC50 < 50 µg/mL) inducing cell death by apoptosis. Two compounds reportedly having cytotoxic activity were identified by mass spectrometry in the petroleum extract of C. gracilior: β-sitosterol and tocopherol. Results suggest that he cytotoxic and pro-apoptotic effects of the petroleum ether extract of C. gracilior could be exerted by the joint activity of β-sitosterol and tocopherol, possibly in combination with of other minor compounds. Because hawthorn is widely consumed in Mexico and Latin America its potential use as a functional food warrants further investigation.